1. Field of the Invention
This invention concerns a new class of polymers which depolymerize upon exposure to radiation. They are useful in making direct positive images and are adapted to the formation of negative images as well.
2. Prior Art
U.S. Pat. Nos. 3,445,234; 3,479,185; and 3,784,557 describe the preparation of hexaarylbiimidazoles and their dissociation in the presence of actinic radiation to 2,4,5-triarylimidazoyl free radicals. The hexaarylbiimidazoles together with an electron donor agent comprise a free radical generating system useful for the photopolymerization of ethylenically unsaturated compounds in photopolymerizable compositions. U.S. Pat. No. 3,445,234 describes image-forming radiation-sensitive compositions which contain a leuco dye and a hexaarylbiimidazole (2,4,5-triarylimidazolyl dimer). No art appears to be known which describes hexaarylbiimidazole-containing polymers or their use in forming images by radiation-induced depolymerization.